The present invention relates to grommets for insulation blankets, and more particularly to grommets for preventing moisture ingress through the blanket.
In aircraft, many system wiring and other attachments must travel through the insulation blankets to secure their equipment to the body of the airplane. The problem is to reliably seal these penetrations as to preserve the functionality of the blanket. Currently in some arrangements, wiring punctures blankets in which a screw connects a P-clamp to the attachment under the blanket. This results in an unsealed blanket allowing water and other liquids to wick into the blanket, which is unacceptable. In some cases, insulation blankets are sealed with a taped construction method to prevent liquid absorption by the batting, which results in significant water weight carried by the airplane. Puncturing these blankets is prohibited due to the tremendous time and cost involved in such insulation construction technique.
A prior attempt to solve this problem was to facilitate the attachment points with a lightweight grommet installed in the blanket at fabrication to allow a P-clamp screw assembly to attach directly onto the attachment. This method relies on a dataset storage area for designers to locate the grommet on the blanket via a template. This is not a practical solution due to factory installation tolerance and incomplete, inaccurate models resulting from late changes. Such placement of the attachments on the airplane in the factory is not accurate enough to reliably match the blankets' pre-installed grommets, resulting in a rejected part or a poor installation.
In the patent literature, U.S. Pat. No. 5,069,586 to Casey describes a two-part self-locking grommet. The grommet comprises an external sleeve and an internal sleeve, each with a formed flange at one end. The bore diameter of the external sleeve is large enough so that the internal sleeve could be inserted, formed flanges at opposite ends. A radiused annular lip is an integral part of the outer diameter of the internal sleeve. When inserted into the external sleeve, the lip snaps into a radiused annular groove and the grommet is locked together. In the case of an aircraft application, an opening for the grommet would need to exist prior to grommet insertion. Prevention of ingress of moisture is not described.
In contrast, the present invention utilizes a two-part snap fit grommet. The snap fit area consists of a sharp annular lip on the internal part which locks into an external washer. One part, hereinafter described, pierces an opening through the material which is to accept the grommet. A retainer is installed onto the piercing part of the grommet, slid down until a snap fit is achieved and the two parts are joined. The piercing tool is then snapped off at a predetermined parting plane located just above the snap fit area.
While aforementioned U.S. Pat. No. 5,069,586 and the present invention utilize a part which snap fits into another part, the patent describes a stand-alone grommet, in contrast to the present invention which is press fit onto a stronger clip or bracket with a standoff. In further contrast, the U.S. Pat. No. 5,069,586 also relies on the prior existence of a hole in the material where it is to be inserted, in contrast to the present integral piercing tool.
U.S. Pat. No. 4,842,465 (Pese, et al.) shows several embodiments of a retaining system whereby an insulation blanket is pushed onto a metal stud which is welded to a wall or support. The stud is machined to a smaller diameter in several places along the length. Insulation is held securely with two retainers that lock onto the stud through a keyhole opening. The stud is left intact after the installation is complete, in contrast to the piercing portion of the present invention which is snapped off at a predetermined fracture plane. The U.S. Pat. No. 4,842,465 utilizes a locking mechanism which relies upon the retainers sliding onto the stud at a section change on the stud. Prevention of moisture ingress is not described. The U.S. Pat. No. 4,842,465 utilizes the principle of snapping on at a section change, but in contrast, in this case the piercing portion has a sharp annular lip and the retainer snaps onto the lip, also. The welded stud shown in the U.S. Pat. No. 4,842,465 is permanent, whereas in the present invention, relocation to a different location is possible.